The invention concerns a screening apparatus and is particularly suitable to and intended for screening machines of the multi-deck type.
The manner in which granular materials are being fed to a screen is of vital influence when it comes to achieving optimum capacity and efficiency.
Normally, screens are fed by means of feeding equipment such as conveyors, screws, vibrating feeders, etc. In such cases a more or less even distribution of the material to be screened is achieved prior to the screening apparatus. Often the material will be fed straight on to the screen cloth or the screening apparatus is equipped with a so-called feeder plate onto which the material is brought in order to protect the screen cloths from wear. The material then falls from this feeder plate onto the screen cloth.
This way of feeding has the consequence that the active screening area is not optimally utilized, because certain areas near the inlet are not engaged or the distribution of the material across the width is uneven. Frequently, the bed of material is thicker in the middle than near the sides so that the centre would be overloaded while the outer parts of the screen cloths could take more load.
Further, the material to be screened, which consists of a mixture of fine and coarse particles, must be segregated in the screening process so that the fine particles can be separated from the coarser ones. This happens relatively slowly and the relative capacities per screening surface area are correspondingly small. As a consequence, screens have to be unnecessarily large.
The invention aims at avoiding the disadvantages above and solves the problem of obtaining screening apparatuses where the material, upon arrival at the screen cloths, is evenly distributed and also already to a certain extent segregated, so that the screen cloths can be optimally used for their purpose and the screening apparatuses can be made much smaller, thereby reducing the screening costs considerably.